Mooring arrangement



2' Sheets-Sheet 1 Filed Aug. 7, 1957 INVENTORS. James G. WalvaordRichqrdvP. Knapp,

Jam 5 1960 R. P. KNAPP Erm. 2,919,671

MOORING ARRANGEMENT Filed Aug. 7, 1957 2 Sheets-Sheet 2 INVENTORS. JamesG. Walvoord, Richard P. Knapp,

#w27-ML( A T TORNE Y United States Patenti/ MooruNo ARRANGEMENT RichardP. Knapp, Houston, Tex., and James G. Walvoord, Grand Isle, La.,assignors, by mesne assignments, to Jersey Production Research Company,Tulsa, Okla., a corporation of Delaware Application August 7, 1957,Serial No. 676,845

Claims. (Cl. 114-230) This invention relates to a mooring arrangement.More particularly, this invention relates to a mooring arrangement forfloating vessels used in conducting 01T- shore operations.

Current mooring arrangements used for floating vessels, such as a rigtender, marine construction vessel, dredge or submarine mining vessel,have several disadvantages. For example, in conducting oifshoreoperations, such as well drilling, a drilling rig platform is used uponwhich the drilling equipment, such as the rigs, motors, etc., areplaced. A oating vessel which is used as a rig tender is moored adjacentthe drilling platform. The usual practice has been to use a plurality ofchains or cables as a mooring arrangement. However, when a storm warningis sounded, it is necessary in order to avoid a collision between thetender and the drilling piatform that certain of the cables or chains bedisconnected. If these chains or cables are not disconnected, there is astrong possibility that the tender will be pushed against the platformby the waves and both damaged severely.

Quite often it happens that storm warnings are given, the'desiredmoorings disconnected from the rig tender; and then no storm occurs. Itis then necessary to recover the disconnected moorings,l and dependingupon the weather conditions, it may take many days to recover thedisconnected moorings. This loss of time is Very costly. If, instead ofdisconnecting the particular mooring lines, all of the lines were leftconnected and a storm did strike, it is highly possible that if themooring lines were allowed to break at random, a collision between thetender and the platform would occur.

Our new mooring arrangement with the new type of mooringmeans utilizedprovides an arrangement which can be used to maintain the tender in thenormal mooring position during calm weather. lf a storm warning isreceived, our new mooring arrangement remains intact. Hence, if thestorm does not actually occur, the mooring means have not beendisconnected and the time lost in recovering lost mooring means issaved. On the other hand, if a storm should occur, the specic structureof certain of the mooring means in the arrangement is such that themooring means will not be allowed to break at random and only thosemooring means will break which will minimize the possibility of acollision between the tender and the platform.

Briefly described, our new mooring arrangement includes a plurality ofmooring means which are connected to anchors spaced about the rigtender. An important feature of the mooring arrangement is that some ofthe mooring means are purposely made with a section thereof strongenough to remain intact in normal weather and yet weak enough to breakin a severe storm. Hence, if a storm should strike, the mooring meanshaving Vthe weak section will be broken by the storm and the tender willswing about on the remaining chains in a manner such that it is keptclear of the drilling platform.

For a detailed description of a preferred embodiment of the invention,reference will be had to the accompanying drawings in which:

Fig. 1 is a plan view showing the mooring arrangement with the rigtender in normal mooring position;

Fig. 2 is a plan view showing the mooring arrangement in storm mooringposition;

Fig. 3 is a plan View of one of the chains containing the frangiblematerial;

Fig. 3a is an elevational view of the chain stopper of Fig. 3; and

Fig. 4 is a plan view showing the relative positions of the steel pilemooring anchors with respect to the drilling platform. A

Referring to Fig. l, a long narrow floating vessel 10 is shown moored inposition adjacent a platform 11. In offshore operations, platform 11contains the necessary equipment for conducting the operations, such asdrilling rigs, engines, pipes, etc., with the vessel 10 used as a`tender. Though vessel 10 is shown as long and narrow, it is to beunderstood that the vessel may be of any other shape, such as a square.

The vessel 16 is moored by means of a plurality of mooring means 12, 13,14, 15, 16, 17, 1S, and 19. Each of the mooring means l2 through 19,inclusive, may consist of a chain consisting of a plurality of chainlinks with each chain being connected to steel pile mooring anchors, 5t)to 57, inclusive. f

Chains 12 and 13 are connected to the aft short side of the vessel andextend outwardly from the aft side. Chains 12 and 13 are normally onopposite sides of a. plane passing through the longitudinal axis of thevessel.. Two other chains 14 and 15 are connected to the aft part of thevessel ltl on opposite long sides of the vessel.Y The remaining fourchains 16 through 19, inclusive, all radiate from the bow of vessel 1)with chains 16 and 17 v extending substantially parallel to chains 14and 15, and chains 13 and 19 extending outwardly from the bow onopposite sidesof a plane passing through the longitudinal axis of thevessel l0. The angular separation of chains.

- 18 and 19-from the longitudinal axis of vessel 10 is suboccurs.

` tice.

stantially greater than the angular separation of chains 12 and 13 fromthe longitudinal axis.

When storm warnings are given, the current practice is to disconnectsome of the mooring chains, such i as chains 14 through 19, inclusive,and shorten 12 and 13 Vso as to be certain that the vessel 10 does notcollide with platform 11. However, as stated, quite often after stormwarnings the storm does not actually occur andl many days may be used inrecovering the disconnected chains. If all of the chains are leftconnected and a storm does occur and certain of the chains are broken bythe i storm, such as chains 12 and 13, it can be seen from Fig. 1 that acollision between the tender 1t) and plat- I form 11 is quite likely. Ithas occurred in actual prac-y This causes severe damage to the platformand equipment thereon and also severe damage to the vessel.

We, however, provide a storm mooring arrangement which need not bedisconnected when a storm warning The new storm mooring arrangement alsoassures that no collision will occur between the tender and theplatform. Our new storm mooring arrangement includes a section offrangible material in some of the chains 12 through 19, inclusive. Thefrangible material is strong enough to remain intact if a storm does notoc'- cur and yet weak enough that breaks will occur at `the points wherethe frangible material is located rather than at other points in thechain.

lA specic embodiment of chain or mooring meansz in which this principleof purposely placing a section in the chain of weaker breaking strengthis illustrated in Fig. 3. A chain guide 2u is shown positioned on thedeck 21 of the tender. The chain is payed-out and reeled in through amooring chock 22. A chain stopper 23 is positioned across the chainguide 2t? and utilized to control the amount of pay-out of the chain. Inthe embodiment shown in Fig. 3, a pair of two inch heavy duty detachablelinks 2S and 2,6 are used to connect the frangible material to the restof the chain. This frangible material may consist of the wrought ironlinks 27, 23, andA 29 shown in Fig. 3. Heavy duty detachable links 25and 26 initially have recesses formed therein for the easy attachmentand detachment of links 27, 28, and 29 from the rest of the chain, theserecesses being closed after attachment of frangible material by variousmeans.

Referring again to Fig. l, which is the normal mooring arrangement, weprovide chains l2 and 13 with a new two inch high strength forged steelchain having a high breaking strength. This increased strength inmooring lines 12 and 13 reduces the probability of collisions betweenthe drilling rig lll and the drilling rig tender 10 as a result ofmooring line failures. Chains 12 and 13 may be anchored to the steelpiles 5G and 51 by means of anchors 32 and 33, respectively. Steel pilemooring anchors through 57, inclusive, are driven into the hard bed ofthe bottom.

The wrought iron links are included in chains 14 through 19, inclusive,and are kept inboard of the chain Stoppers when the vessel is in normalmooring posiing position. Hence, during normal mooring operations thefrangible material is not subject to the forces of the Wind and the waveand, hence, there is no possibility that a chain will break at thefrangible material during normal operations.

By using wrought iron links of the same size as the forged steel linksin the remainder of the mooring chain, handling of the mooring linesthrough chocks and chain stoppers is facilitated.

If a storm warning occurs, the vessel is moved away from platform 11about 200 more feet so as to be approximately 225 feet from the frontedge of the platform. The changed relative position of the mooring means1 2 through 19, inclusive, is as shown in Fig. 2. The wrought iron linkshave been allowed to pay-out along with the chains 14 through 19,inclusive, so that during storm mooring arrangement they are outboard ofthe vessel such as shown in Fig. 3. The breaking strength of the wroughtiron chain links may vary in magnitude from just below the breakingstrength of the forged steel links to less than half the breakingstrength of the forged steel links. Using the same materials for thestrong and weak sections, the breaking strengths vary according to chainsize and size of the tender. The breaking strength of the wrought ironlinks is high enough so that if the storm does not strike they willremain intact and it will not be necessary to connect them again. If astorm should strike and is of suicient severity, any breakage of themooring lines will occur at the weak links. After the wrought iron linkshave been broken, chains 14 through 19, inclusive, will no longerrestrain the movement of the vessel it). Thus, after the breaking of thechains, the vessel l@ will swing on the chains 12 and 13 regardless ofthe direction or change in direction of the wind. The longitudinal axisof the vessel 10 will continuously be aligned with the direction of thewind. ecause the longitudinal axis of the vessel is aligned with thisdirection, the smallest area of the vessel is always presented towardthe main force of the winds and waves. Also, no restraint is maintainedon the pivotal movement of the vessel l@ about the piles 50 and 5l.Thus, the stress upon chains l2 and 13 is minimized. Hence, chains 12and 13 will remain intact i and the vessel will be retained out of reachof platform Fig. 4 is a plan view showing the angular relationship ofthe steel pile mooring anchors with respect to the front of platform iland the longitudinal axis of platform Ill. Piles 5@ and 5l are at 2 40on opposite sides of the longitudinal axis, piles 52 and 53 are atapproximately 68 47 on opposite sides of the longitudinal axis, piles 54and 55 are at approximately 87 6' on opposite sides of the longitudinalaxis, and piles 56 and 57 are at 132 lll/2 on opposite sides of thelongitudinal axis.

in operation, the vessel l@ is maintained at about 25 feet away fromplatform 11 with the bow facing the platform. if a storm warning occurs,the vessel is moved from the platform another 200 feet. rhe movement isaccomplished by pulling in chains 12 and i3, lifting chain stopper 23,and paying-out the chains 14 through 19, inclusive. The frangible linkswhich, during normal mooring arrangement, are inboard are then passedthrough the chain stopper so that they are placed outboard and thechains locked by setting the appropriate chain stopper and the brake onthe chain windlass.

We create weak spots of a selected magnitude lin the mooring means. Theweak spots are illustrated as being weak links, such as links made ofwrought iron. In some cases, links of cast steel might be used. Also,forged steel links of material identical with the remainder of themooring means, but of a different size or partly sawed through, might heused. Accordingly, the term frangible as used herein and in the appendedclaims is intended to include the use of any material and any` physicalconfiguration to produce the desired degree of weakness.

We claim:

l. A mooring arrangement for a long, narrow floating vessel comprising:four anchored mooring chains radiatf ing from each end of the vessel,with two of said four mooring chains extending outwardly from the shortside of the vessel, one on each side of a vertical plane passing throughthe longitudinal axis of the vessel and the other two mooring chainsextending from opposite long sides of the vessel, at least one of saidtwo mooring chains extending outwardly from one short side of the vesselbeing made up of chain links of high breaking strength throughout theirlength and the other mooring chains each having at least one weak linkhaving a breaking strength of less than one-half the breaking strengthof the rest of the chain links; means for retaining the weak linksinboard when the vessel is in normal mooring position and means forpaying out the weak links outboard when the vessel is moved to stormmooring position.

2. A storm mooring arrangement for a oating vessel comprising: twoanchored mooring means each having la high breaking strength along theirentire length and extending outwardly from the stern side of thevessel;` and a plurality of other anchored mooring means radiating fromthe other sides of the oating vessel and each having a portion offrangible material of substantially lower breaking strength than therest of the mooring means.

3. A storm mooring arrangement in accordance with claim 2 wherein saidplurality of mooring means are chains and the portion of frangiblematerial consists of at least one link of wrought iron with the rest ofthe chains consisting of forged steel links.

4. A storm mooring arrangement in accordance with claim 3 wherein thewrought iron has a breaking strength of lless than one-half the breakingstrength of the forged stee 5. A storm mooring arrangement in accordancewith claim 2 wherein said two anchored mooring means are chains offorged steel along their entire length with one chain being on each sideof a vertical plane pasing nthrough the longitudinal axis of thevessehand the plural# ity of other anchored mooring means includes'sixchains of' forged steel with each chain having a portion thereof ofReferences Cited in the file of this patent wrought iron, with two ofsix chains radiating from the same end of the vessel as the two chainsmade of forged FOREICI PATENTS steel along their entire length, and fourof said six 2,543 Great Britain of 1871 chains radiating from the otherend of the vessel. 5 668,786 Germany Dec. 9, 1938

